1. Field of the Invention
Embodiments of the invention relates to a method, system and computer program product for monitoring patient's breathing action response to changes in a ventilator applied breathing support, and in addition for assessing a readiness of a patient to be weaned from a ventilator in a weaning process and for adjusting the ventilator applied breathing support.
2. Description of Prior Art
Weaning the patients from artificial ventilation is among the most difficult questions regarding intensive care ventilation. Patients encountering weaning problems have often been ventilated to cure from the primary illness more than 48 hours before the ventilator weaning can be considered. Within the stay on ventilator support some patients develop ventilator dependency and they cannot maintain breathing of their own. This dependency may prolong the stay on ventilator therapy manifold in comparison with that needed for curing the primary illness. Prolonged ventilation increases risk for lung inflammation known as ventilator induced lung injury (VILI). Even worse, inflammatory mediator may spread from the lungs to other organs developing multiple-organ-failure. Mortality of those patients is high. Therefore, minimizing the stay on ventilator is primary goal for intensive care.
Methods for assessing the readiness for weaning are known from the prior art. However, assessing the readiness for weaning varies between clinics and so does the average stay on ventilator as well. Studies of current practices have revealed that lack of intensive care personnel correlates with delayed weaning promoting the need for systematic process to wean from ventilator. Clinical research on such processes focuses on three separate weaning phases: (1) screening to assess curing from primary illness indicating readiness to consider weaning, (2) evaluate patients ability to maintain sufficient gas exchange without ventilator support, and (3) extubation.
Screening proposals are often based on a set of laboratory and respiratory parameters that have to stay within specified range to consider weaning. To evaluate patient's ability to breath without ventilator various prior art protocols are used, like stepwise ventilator support reduction, or T-tube trial, where patient is just disconnected from ventilator. The prior art methods however share the problem of sensitive indicators. Final decision to extubate the patient depends finally on patient's ability to maintain airways open.
Reasons contributing to weaning problems have also been on clinical research. One leading hypothesis is respiratory muscle atrophy that develops rapidly in the unused muscles during artificial ventilation. Spontaneous breathing supports maintenance of muscular strength, but on sedated patient this requires continuous regulation of the ventilator support for moderate exercise level. For this purpose automatic control of ventilator settings based on measured patient values have been introduced (Dojat M, Harf A, Touchard D, Lemaire F, Brochard L: Clinical Evaluation of a Computer-controlled Pressure Support Mode Am J Respir Crit. Care Med Vol 161. pp 1161-1166, 2000). This prior art system regulates the ventilator support pressure to maintain spontaneous breathing frequency as primary control parameter on preset range, and tidal volume above minimum level as well as end-tidal CO2 concentration below maximum as limiting parameters. Basically in this kind of systems the pressure support is increased if the breathing frequency will be too fast, and decreased, if the breathing frequency will be too slow, respectively. However, the prior art system also automatically suggest considering weaning from ventilator when the ventilator support pressure reduces below predetermined limit for predetermined time.
There are, however, some disadvantages relating to the prior art systems, such as the vague correlation of respiration rate or frequency to the gas exchange the ventilation should maintain. Assessing the respiration frequency could be comfortable when considering the average of number of patients, but often not for an individual patient. This may overstress a patient and delay the weaning unnecessarily. Therefore the prior art method cannot be applied on difficult to wean patients.